1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor device and, more specifically, to a method of removing residual carbon deposits from an intermediate semiconductor device structure.
2. State of the Art
Performance of semiconductor devices has increased dramatically over the past few years as a result of increased circuit density on a semiconductor substrate. As the density of the semiconductor devices has increased, it has become necessary to decrease the size of circuit components that form the semiconductor devices so that the necessary number of circuit components is able to fit on the semiconductor substrate.
Semiconductor devices typically include the semiconductor substrate and a plurality of adjacent, active devices that are electrically isolated from one another. With the increased circuit density, effective isolation between active devices becomes increasingly important. One isolation technique is local oxidation of silicon isolation (“LOCOS”), which forms a recessed oxide layer in nonactive regions of the semiconductor substrate to isolate the active devices. The oxide layer is formed by sputtering techniques or thermal techniques.
An alternative technique is trench isolation, which involves etching trenches in the nonactive regions of the semiconductor substrate. Trench isolation is referred to as shallow trench isolation (“STI”) or deep trench isolation (“DTI”), depending on the depth of the trench etched in the semiconductor substrate. DTI structures, which typically have a depth of greater than approximately 3 microns, are used to isolate active devices such as N-wells and P-wells. Shallow trench structures are used to isolate adjacent electronic devices, such as transistors, and have a depth of less than approximately 1 micron. The trenches are filled with an insulative dielectric material, such as a silicon dioxide material. The filled trenches are known in the art as trench isolation or trench isolation regions. The trench is typically filled with the silicon dioxide material by a chemical vapor deposition (“CVD”) technique, such as high density plasma (“HDP”) CVD. In CVD, gaseous precursors of the silicon dioxide material are supplied to a surface of the semiconductor substrate. The gaseous precursors react with the surface to form a film or layer of the silicon dioxide material.
Trench isolation provides a smaller isolation area and better surface planarization than LOCOS. While trench isolation provides these advantages, undesirable voids are formed in the silicon dioxide material as the trench fills because the silicon dioxide material sticks to the sides and sidewalls of the trench, rather than evenly filling the trench from the bottom to the top. Voids are especially common in deep trenches, such as trenches having a high aspect ratio of greater than approximately 3:1. Voids also commonly form at later stages of the filling process because the trenches, both deep and shallow, become narrower as they fill.
As disclosed in Chung et al., “Novel shallow trench isolation process using flowable oxide CVD for sub-100 nm DRAM,” IEEE (2002), CVD of flowable oxide materials has been used in combination with HDP CVD to reduce the formation of voids. A liquid Si(OH)4 film is formed in the trench by supplying silane and hydrogen peroxide (“H2O2”) to a surface of the substrate. The Si(OH)4 film is covered with an HDP oxide to protect the Si(OH)4 film from severe cleaning conditions.
In addition to being used in shallow trenches, CVD of flowable oxide materials is useful to fill trench structures having a high aspect ratio. While depositing the flowable oxide material by CVD reduces the formation of voids, residual carbon deposits are present in the deposited film if the gaseous precursors contain carbon. Carbon in the deposited film causes the film to be soft and porous, which makes the deposited film unstable during subsequent processing, such as etching processes. Since the deposited film is porous, due to the presence of the carbon, it also tends to collapse. In addition, if the flowable oxide material is used to fill isolation trenches, the carbon causes device degradation.
It would be desirable to reduce or eliminate the residual carbon deposits present in deposited layers of flowable oxide materials.